Two Boulder scientists have published an analysis of leading climate models that indicates those predicting a greater rise in global temperatures are likely to be more accurate than those showing a lesser increase.

National Center for Atmospheric Research scientists John Fasullo and Kevin Trenberth analyzed the accuracy of sophisticated climate models to measure relative humidity in the tropics and subtropics. The study appears in this week's issue of Science.

According to a news release issued by NCAR on Thursday, complex moisture processes such as relative humidity and associated cloud activity have a significant impact on global climate. Because cloud activity is difficult to measure via satellite, the study focused on how accurately climate models measured relative humidity in the subtopics during the dry season.

Using the May-through-August season, which brings clear skies to the southern subtropics -- allowing for more heat from the sun during the day as well as more heat to escape Earth's atmosphere by night -- as a proxy for climate change, Trenberth said, the study evaluated each model's accuracy. The study found that those models that predicted less warming due to greenhouse gases in the future were also the least accurate when it came to measuring relative humidity in those zones, leading the authors to conclude they would be less reliable moving forward.

"They don't satisfy this metric," Trenberth said. "They don't have the right characteristics of humidity and clouds and their variation for the seasonal cycle, so we can rule those models out."

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The benchmark for comparing climate model projections is called equilibrium climate sensitivity, according to NCAR. It dictates how much warmer the Earth will be once the level of atmospheric carbon dioxide reaches double its pre-industrial levels, which is expected to occur before the year 2100, according to NCAR.

Of 16 major climate models analyzed in the study, all of which were used for 2007-08 assessment by the Intergovernmental Panel on Climate Change, that value averaged an increase of around 5 degrees Fahrenheit, but went as low as 3 degrees warmer and as high as 8 degrees warmer.

Based on the relative humidity metric, those models predicting a 7-degree increase and above appear to be the most accurate, according to the study.

Trenberth emphasized the study focuses on one aspect of global climate modeling that must be assessed to ensure accuracy. He noted there are many other elements of the global climate that must be captured by the models to make sure they are providing the best picture of climate change, and he and his colleagues will be busy assessing those in coming years.

"This study does not pin it down," he said. "This is just one aspect of things that models need to get right, and if they get it wrong then we don't have confidence in them."

For Trenberth, the importance of having accurate climate projections has been embodied this year by events such as superstorm Sandy, the summer heat wave across the U.S. and the record Colorado wildfire season.

"This relates to the magnitude of the problem that we are facing moving into the future," he said. "If we were at the low end (of temperature increase), then maybe we could go with the flow. We're suggesting here, then, that climate change is apt to be much more disruptive, and maybe we are seeing some aspects of that already.

"We need to worry about these more as we go into the future, which means consideration about what to do about it terms of slowing it down and planning for the consequences."